Happy Wednesday and welcome to Overnight Defense. I'm Rebecca Kheel, and here's your nightly guide to the latest developments at the Pentagon, on Capitol Hill and beyond. CLICK HERE to subscribe to the newsletter.

"The joint resolution would raise serious constitutional concerns to the extent that it seeks to override the President's determination as Commander in Chief," the White House Office of Management and Budget (OMB) said.

What's next: The resolution still needs to pass the House before it heads to Trump's desk. Senate supporters believe it could get a vote in the lower chamber as soon as Thursday, paving the way for potentially the first veto of Trump's presidency.

"Our office is working with leadership and the [Congressional Progressive Caucus] to finalize a date of when we will pass the Senate [War Powers Resolution] and send it to the president's desk," his office added.

A rough week for Trump: Wednesday's vote comes a day before the Senate is likely to also pass a resolution of disapproval blocking Trump's emergency declaration -- setting up a one-two punch that will force the president to reject back-to-back legislation from Capitol Hill.

The big picture: Saudi Arabia has emerged as a growing split between Trump and Congress in the wake of the slaying last fall of Washington Post contributor Jamal Khashoggi, who was a critic of the Saudi government.

Trump has refused to pin the blame of Khashoggi's death on Saudi Crown Prince Mohammed bin Salman, saying in a widely panned statement late last year that "maybe he did and maybe he didn't" order the slaying. Trump added that the U.S. "may never know all of the facts surrounding the murder" of Khashoggi.

Trump's stance has put him at odds with Republicans in Congress as well as his own intelligence community, which has reportedly determined that the Saudi crown prince ordered the killing of Khashoggi.

At issue is Shanahan's former job as a Boeing executive and accusations that he's used his perch in the Pentagon to promote the defense contractor.

On Wednesday, Citizens for Responsibility and Ethics in Washington (CREW) asked the Department of Defense Inspector General (DODIG) to look into Shanahan.

CREW has asked DODIG to find out if Shanahan has violated his own ethics pledge to recuse himself from matters dealing with Boeing.

The allegations: The complaint alleges that Shanahan "made numerous statements promoting his former employer Boeing and has disparaged the company's competitors before subordinates at the agency."

"In private remarks he made since then at DoD, Mr. Shanahan reportedly praised Boeing in discussions about government contracts, said that Boeing would have done much better than its competitor Lockheed Martin had it been awarded a fighter jet contract, and repeatedly 'dumped on' the jet Lockheed produced," according to the complaint.

Among the major accusations, CREW writes that Shanahan pressed the Air Force to include in its fiscal 2020 budget an unwanted purchase of Boeing-made F-15Xs.

The Pentagon on Tuesday revealed its fiscal year 2020 budget request which includes eight of the fourth-generation fighter jets for about $1.1 billion -- DOD's first F-15 buy since 2001 -- and plans to buy up to 72 more in the next five years.

The denial: A statement from Shanahan's office on Wednesday denied any ethics violations.

"Secretary Shanahan has at all times remained committed to complying with his Ethics Agreement, which screens Boeing matters to other DoD officials and ensures no potential for a conflict of interest with Boeing on any matter. Secretary Shanahan remains focused on aligning the Department along the National Defense Strategy," according to his spokesman Army Lt. Col. Joe Buccino.

Boeing woes: Boeing has also been in the public eye due to two fatal crashes within five months -- the latest of which was on Sunday -- involving its commercial passenger jet, the Boeing 737 Max 8. The most recent crash, involving an Ethiopian Airlines plane, killed all 157 people on board, while a Lion Air crash in Indonesia last October killed 189 people.

Shanahan's time at Boeing includes working as the senior vice president of airplane programs at Boeing Commercial Airplanes, where he oversaw the 737, 747, 767, 777 and 787 programs.

Asked on Tuesday by CNN about the MAX-8 crashes, Shanahan said, "Let's let the FAA and others take command of the situation."

Shanahan's next test: Shanahan will likely be asked to answer for CREW's letter when he appears before the Senate Armed Services Committee on Thursday morning.

The hearing is Shanahan's first since becoming acting secretary, and he's likely to be grilled on a host of defense issues from Syria to North Korea to transgender troops.

The appearance is widely being seeing as a make-or-break moment in Shanahan's audition to be the permanent Defense secretary.

Asked Wednesday whether he will nominate Shanahan, Trump said he is "doing a fantastic job" in the acting role.

PENTAGON MOVES FORWARD ON TRANSGENDER BAN: If you missed it last night while you were watching The Bachelor finale, the Pentagon is implementing its policy to ban most transgender people from serving in the military.

A memo signed Tuesday night by acting Deputy Defense Secretary David Norquist says the policy will go into effect on April 12.

Under the policy, transgender people who join after it takes effect will have to serve in the gender they were assigned at birth. Service secretaries will be allowed to grant waivers on a case-by-case basis.

The specifics: The policy will grandfather in currently serving transgender troops or anyone who has already signed an enlistment contract, allowing them to continue serving openly.

But after April 12, people diagnosed with gender dysphoria will not be able to serve unless a doctor certifies they have been stable in their biological sex for 36 months, have not transitioned to the gender they identify with and are willing to serve in their biological sex.

If they are diagnosed after they join the military, they have to continue serving in their biological sex.

Troops diagnosed with gender dysphoria can be discharged if they are "unable or unwilling to adhere to all applicable standards, including the standards associated with their biological sex," the memo says.

Pentagon says it's not a ban: In a background call with reporters Wednesday, defense officials repeatedly insisted the policy is not a ban.

They point to the fact that currently serving transgender troops can continue doing so and that only transgender people diagnosed with gender dysphoria will be barred from enlisting.

"Merely identifying as transgender has no practical military consequence," an official said.

"I really don't get any logic to how this gets you to this is a ban on transgender service," the official added later.

But transgender people and their advocates say it effectively is a ban akin to "Don't Ask, Don't Tell." By saying transgender people can serve if they haven't been diagnosed with gender dysphoria and serve in their biological sex, the argument goes, the Pentagon is effectively saying transgender people can serve if they hide who they are.

Congress reacts: Democratic lawmakers slammed the Pentagon starting Tuesday night and into Wednesday for moving forward on the policy.

"Any other course of action not only undermines military readiness, but is also an insult to transgender individuals who have served and are still serving with distinction," he said in his statement. "Anyone who is qualified and willing should be allowed to serve their country openly. Make no mistake, this is a discriminatory ban on transgender people, not a ban on a medical condition and we will continue to fight against this bigoted policy."

"There are thousands of transgender Americans serving in our Armed Forces today with courage, honor, and distinction," Reed said in his statement. "Our troops defend the rights and freedoms of all Americans. We must not allow bigotry to impede our military's critical mission."

SPACE FORCE ROADBLOCK: As lawmakers digest the White House's Space Force proposal and begin thinking about this year's annual defense policy bill, House Armed Services Committee Chairman Adam Smith (D-Wash.) is indicating his committee will take a different path.

Speaking at a Washington conference, Smith said what the House Armed Services Committee is going to do is will be "different from what the White House proposed."

"I cannot imagine that what they proposed is going to happen," Smith said at the McAleese & Associates conference in Washington, D.C.

"It's too expensive and creates more bureaucracy. We don't want to just, you know, create more people. We want to figure out how to better emphasize space."

His major complaint was the added bureaucracy the new military branch will create.

"We don't need three more four-star generals," Smith said, referring to the administration's move to create several new, high-ranking positions to lead the new Space Force and U.S. Space Command. "Three more four-star generals are not going to make us stronger in space."

The budget also requests $83.8 million to stand up Space Command and $149.8 for the newly created Space Development Agency.

The total effort is expected to cost $2 billion over the next five years.

Air Force response: Air Force Secretary Heather Wilson, when asked about Smith's remarks, told reporters on Capitol Hill that she looks forward to working with him "and identifying what's important to him and how we can move forward on space."